linux-kernel - Re: [PATCH RFC] USB: Add HCD fastboot

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Message-ID: <20080806192913.GA29239@suse.de>
Date:	Wed, 6 Aug 2008 12:29:13 -0700
From:	Greg KH <gregkh@...e.de>
To:	Simon Arlott <simon@...e.lp0.eu>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Rene Herman <rene.herman@...access.nl>,
	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org, mingo@...e.hu,
	Daniel Walker <dwalker@...sta.com>,
	USB list <linux-usb@...r.kernel.org>
Subject: Re: [PATCH RFC] USB: Add HCD fastboot

On Wed, Aug 06, 2008 at 08:20:13PM +0100, Simon Arlott wrote:
> On 06/08/08 20:11, Alan Stern wrote:
>> On Wed, 6 Aug 2008, Simon Arlott wrote:
>>> On 31/07/08 20:16, Alan Stern wrote:
>>> >> > It's not entirely clear why usblp is blocking at all.  Probably 
>>> because
>>> >> > it is waiting on the device semaphores for devices that are 
>>> currently
>>> >> > being probed -- the driver core won't allow two threads to probe the
>>> >> > same device concurrently.
>>> >> >> Ok - so there could be some big improvements to be had by making 
>>> the hcd >> init happen as early as possible and the device initcalls 
>>> later?
>>> > > Maybe.  Perhaps a better approach would be to make the device driver 
>>> > initcalls before there are any devices for their probe routines to > 
>>> block on.
>>> What about this?
>>> The Makefiles become a bit messy, but by moving things around I get the 
>>> desired effect without splitting their initcalls.
>> Wouldn't it be much simpler, and less objectionable, to do what I
>> suggested earlier?  That is, add a 5-second delay at the start of
>> hub_thread() in drivers/usb/core/hub.c.  No messing with Makefiles, no
>> changes to the initcall scheduling.
>
> Aside from 5 seconds being too long, and anything less being a race between 
> hub_thread() and driver initcalls, it doesn't improve anything because 
> it'll still have to wait for the devices to finish initialising in 
> userspace instead.

And what is your boot time if the usb drivers are modules?

I'd much prefer that requirement to get a faster boot than to go around
mucking with the link-time ordering...

thanks,

greg k-h
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